Sensor arrangement for position sensing

ABSTRACT

A sensor arrangement for position sensing comprises a row of multiple magnetoresistive elements. A magnetic field source ( 3 ) provides a magnetic field with a first magnetic pole (N) and a second magnetic pole (S). The magnetic field source ( 3 ) is arranged such that magnetoresistive elements of the row face one of: the first magnetic pole (N) or second magnetic pole (S). The first magnetoresistive element is arranged in the magnetic field and provides a first output signal dependent on a position of the magnetoresistive element relative to the magnetic field source ( 3 ). A measurement unit is configured to determine a position of the magnetic field source ( 3 ) relative to the magnetoresistive elements of the row dependent on the first output signals of the magnetoresistive elements.

FIELD OF THE INVENTION

The present invention relates to a sensor arrangement for positionsensing and to a method for supporting determining the position of anobject.

BACKGROUND

High bandwidth, high resolution nanoscale sensing is a key enablingtechnology for nanoscale science and engineering. Application areasinclude life sciences, scanning probe microscopy, semiconductorfabrication and material science. Currently available position sensorsbased on optics, capacitors or inductive coils, although accurate andfast, do not scale down to micro-scales for use in micro-structures orin large-scale point-wise position sensing of macro-structures.Thermo-electric position sensors, on the other hand, scale down tomicro-scale, but suffer from low resolution and bandwidth.

A known position sensing concept is based on the property ofmagnetoresistance (MR). Magnetoresistance is the property an electricalresistance of a conductive layer sandwiched between ferromagnetic layerschanges as a function of a magnetic field applied to the layers. Amagnetoresistive sensor typically uses this property to sense themagnetic field.

BRIEF SUMMARY OF THE INVENTION

According to an embodiment of one aspect of the invention, a sensorarrangement is provided for position sensing. The sensor arrangementcomprises a first magnetoresistive element, a second magnetoresistiveelement, and a magnetic field source providing a magnetic field with afirst magnetic pole and a second magnetic pole. The magnetic fieldsource is arranged between the first magnetoresistive element and thesecond magnetoresistive element with the first magnetic pole facing thefirst magnetoresistive element and the second magnetic pole facing thesecond magnetoresistive element. The first magnetoresistive element isarranged in the magnetic field and provides a first output signaldependent on a position of the first magnetoresistive element relativeto the magnetic field source. The second magnetoresistive element isarranged in the magnetic field and provides a second output signaldependent on a position of the second magnetoresistive element relativeto the magnetic field source. A measurement unit is configured todetermine a position of the magnetic field source relative to the firstand the second magnetoresistive element dependent on the first outputsignal and the second output signal.

In embodiments, the sensor arrangement may comprise one or more of thefollowing features:

-   -   each of the magnetoresistive elements comprises a stack of        layers including at least a conductive layer in between two        magnetic layers which layers have a longitudinal extension along        a longitudinal axis and a lateral extension along a transverse        axis,    -   the magnetic field source has a dipole axis defined by the first        and the second magnetic pole extending along a vertical axis        orthogonal to a plane defined by the longitudinal axis and the        transverse axis,    -   the magnetic field source is movable relative to the first and        second magnetoresistive element along the longitudinal axis, a        position thereof along the longitudinal axis is to be sensed by        the sensor arrangement,    -   the measurement unit is configured to determine the position        along the longitudinal axis by adding the first output signal        and the second output signal,    -   the magnetic field source is movable relative to the first and        second magnetoresistive element along the vertical axis, a        position thereof along the vertical axis is to be sensed by the        sensor arrangement,    -   the measurement unit is configured to determine the position        along the vertical axis by computing a difference between the        first output signal and the second output signal,    -   multiple first magnetoresistive elements arranged in the        magnetic field in a row along the longitudinal axis and facing        the first magnetic pole,    -   multiple second magnetoresistive elements arranged in the        magnetic field in a row along the longitudinal axis and facing        the second magnetic pole,    -   the magnetic field source is dimensioned relative to the        multiple first magnetoresistive elements such that the magnetic        field only affects a single of the multiple first        magnetoresistive elements at a time but not adjacent first        magnetoresistive elements,    -   the magnetic field source is a permanent magnet which has a        width less than the longitudinal extension of the first        magnetoresistive elements,    -   the measurement unit is configured to identify the single first        magnetoresistive element out of the multiple magnetoresistive        elements that shows a change in its first output signal which        change results from the magnetic field source passing by the        single first magnetoresistive element,    -   the measurement unit is configured to derive the position along        the longitudinal axis from a known position of the single first        magnetoresistive element within the row of the multiple first        magnetoresistive elements.    -   the magnetic field source is dimensioned relative to the        multiple first magnetoresistive elements such that the magnetic        field not only affects a single of the multiple first        magnetoresistive elements but also adjacent first        magnetoresistive elements,    -   the magnetic field source is a permanent magnet which has a        width along the longitudinal axis exceeding the longitudinal        extension of the first magnetoresistive element,    -   a magnetization orientation of both of the magnetic layers of        the multiple first magnetoresistive elements is unpinned,    -   the measurement unit is configured to subtract first output        signals of adjacent first magnetoresistive elements from each        other,    -   the measurement unit is configured to determine the position        along the longitudinal axis dependent on a resulting difference        signal,    -   a magnetization orientation of one of the magnetic layers of the        multiple first magnetoresistive elements is pinned,    -   the measurement unit is configured to add the first output        signals of adjacent first magnetoresistive elements,    -   the measurement unit is configured to determine the position        along the longitudinal axis dependent on a resulting sum signal,    -   the multiple first magnetoresistive elements are arranged in the        row are offset from each other along the vertical axis,    -   a middle first magnetoresistive element is arranged at a closest        vertical distance from the magnetic field source amongst the        multiple first magnetoresistive elements of the row,    -   outmost first magnetoresistive elements are arranged at a        farthest vertical distance from the magnetic field source        amongst the multiple first magnetoresistive elements of the row,    -   one of the magnetoresistive elements and the magnetic field        source is coupled to an object, the position of which object is        to be sensed by the sensor arrangement.

According to an embodiment of another aspect of the present invention, amethod is provided for supporting determining the position of an object.One of a magnetic field source providing a magnetic field with a firstmagnetic pole and a second magnetic pole and a first and a secondmagnetoresistive element is coupled with the object. The magnetic fieldsource is arranged between the first magnetoresistive element and thesecond magnetoresistive element with the first magnetic pole facing thefirst magnetoresistive element and the second magnetic pole facing thesecond magnetoresistive element. Output signals are received from thefirst and the second magnetoresistive elements dependent on theirposition relative to the magnetic field source. A position of the objectis determined dependent on the first output signal and the second outputsignal.

Embodiments described in relation to the aspect of the position sensorshall also be considered as embodiments disclosed in connection with anyof the other categories such as the method.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its embodiments will be more fully appreciated byreference to the following detailed description of presently preferredbut nonetheless illustrative embodiments in accordance with the presentinvention when taken in conjunction with the accompanying drawings. Thefigures are illustrating:

FIG. 1 a block diagram of a sensor arrangement according to anembodiment of the present invention,

FIG. 2 diagrams illustrating an impact of a magnetic field on amagnetoresistive element according to an embodiment of the presentinvention,

FIG. 3 a diagram illustrating an impact of a magnetic field on amagnetoresistive element according to an embodiment of the presentinvention,

FIG. 4 a block diagram of a sensor arrangement according to anembodiment of the present invention,

FIG. 5 a diagram illustrating the effect of adding the output signals ofthe first and the second MR elements, as is performed in the sensorarrangement of FIG. 4,

FIG. 6 a block diagram of a sensor arrangement according to anotherembodiment of the present invention,

FIG. 7 a diagram illustrating the effect of subtracting the outputsignals of the first and the second MR elements, as is performed in thesensor arrangement of FIG. 6,

FIG. 8 a block diagram of a sensor arrangement according to a furtherembodiment of the present invention,

FIG. 9 a diagram illustrating the effect of subtracting the outputsignals of the first MR elements, as is performed in the sensorarrangement of FIG. 8,

FIG. 10 a block diagram of a sensor arrangement according to a furtherembodiment of the present invention,

FIG. 11 a diagram illustrating the effect of subtracting the outputsignals of the first MR elements, as is performed in the sensorarrangement of FIG. 11,

FIG. 12 a characteristic of an MR element with and without a pinnedmagnetic layer,

FIG. 13 a diagram illustrating the effect of subtracting the outputsignals of multiple first MR elements with a pinned magnetic layer,

FIG. 14 a block diagram of a sensor arrangement according to a furtherembodiment of the present invention,

FIG. 15 a characteristic of the sensor arrangement of FIG. 14,

FIG. 16 a block diagram of a sensor arrangement according to anotherembodiment of the present invention, and

FIG. 17 a block diagram of a sensor arrangement according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As an introduction to the following description, it is first pointed ata general aspect of the invention concerning a sensor arrangement basedon the magnetoresistive effect.

A magnetoresistive sensor preferably comprises a magnetoresistiveelement comprising a stack of layers which stack of layers includes atleast a conductive layer in between two magnetic layers, and preferablyin between two ferromagnetic layers. Specifically, the magnetoresistiveelement is a giant magnetoresistive element based on the underlyingeffect wherein in a layer stack comprising a non-magnetic conductivelayer sandwiched between two ferromagnetic layers a change in theelectrical resistance can be observed subject to a magnetizationorientation in the ferromagnetic layers. In the absence of an externalmagnetic field, the magnetization orientation of the correspondingferromagnetic layers is antiparallel. By means of applying an externalmagnetic field to at least one of the ferromagnetic layers the subjectmagnetization orientation is changed which in turn leads to themagnetization orientation in the two ferromagnetic layers becomesparallel which in turn causes the electrical resistance of the layerstack to change. The electrical resistance of the layer stack is alsodenoted as electrical resistance of the magnetoresistive element. Thechange in the electrical resistance may be monitored and taken as ameasure for the presence of an external magnetic field applied. Whensuch external magnetic field is generated by a magnetic field sourceattached to an object, a position of such object may be determined withrespect to the magnetoresistive element. Specifically, a significantchange of the electrical resistance in the conductive layer can beobserved when the magnetization orientation of the ferromagnetic layersis changed between a parallel alignment to an antiparallel alignment orvice versa. In a parallel alignment of the magnetization orientation ofthe ferromagnetic layers the electrical resistance in the conductivelayer is rather low while in an antiparallel alignment of themagnetization orientation of the ferromagnetic layers the electricalresistance in the conductive layer is rather high. The change inconductivity is based on spin-dependent interfacial electron scattering.Electrons passing the magnetoresistive element may show a short meanfree path at antiparallel magnetization orientation in the ferromagneticlayers owed to an increased spin dependent electron scattering at theinterfaces between the conductive layer and the ferromagnetic layerswhile electrons may show a longer mean free main path owed to a lessspin dependent interfacial electron scattering when the ferromagneticlayers show a parallel magnetization orientation.

The magnetoresistive element hence preferably comprises a stack oflayers which at least includes one conductive layer in between twoferromagnetic layers, but which stack of layers may include multipleconductive layers sandwiched between adjacent ferromagnetic layers,wherein an overall electrical resistance of the stack of layers mayfinally be measured and allow for a determination of the position of thefield generating magnet relative to the magnetoresistive element. Anexternal magnetic field applied may cause the magnetization orientationin these ferromagnetic layers to switch from an antiparallel alignmentto a parallel alignment or vice versa. Generally, and specifically forthe present embodiments of the invention, the magnetization orientationof both ferromagnetic layers may be floating or, alternatively, themagnetization orientation of one of the ferromagnetic layers may bepinned such that its magnetization orientation may not change even underthe application of an external magnetic field. The external magneticfield may then only act on the other ferromagnetic layer and cause itsmagnetization orientation to change subject to a position the magnettakes.

In the context of the present embodiments of the invention, thefollowing geometrical definitions are used: The layers of the layerstack may have a longitudinal extension along a longitudinal axis and alateral extension along a transverse axis. Accordingly, a height of thestack extends orthogonal to a plane defined by the longitudinal and thetransverse axis along a vertical axis. A sensor central axis of themagnetoresistive element is defined as an axis along the vertical axis,and at half of the longitudinal extension of the layers. It ispreferably assumed that a magnetic field source and/or an objectcomprising the magnetic field source is at least movable along thelongitudinal axis, which means that the magnetic field source is movablealong the longitudinal extension of the layers of the layer stack.Preferably, the magnetic field source is arranged at a vertical distanceD>0 from the magnetoresistive element such that the magnet field sourceand an upper surface of the magnetoresistive element are spaced apartalong the vertical axis by the distance D. Moreover, the magnetic fieldsource provides a magnetic field with a North (N) and a South (S) pole.A dipole axis is assumed to be a straight connection between the N poleand the S pole.

In conventional magnetoresistive position sensing concepts a dipole axisof the magnetic dipole of the magnet is aligned in parallel to alongitudinal extension of the layers of the layer stack contributing tothe magnetoresistive element. Given that a gradient of the magneticfield is responsible for generating a change in the magnetizationorientation of the one or more ferromagnetic layers, it was observedthat in the conventional concept the gradient of the magnetic fieldalong the longitudinal extension of the layers of the stack is ratherlow. The gradient is defined as a change in magnetic flux at anylocation. However, the higher the gradient of the magnetic field isalong the longitudinal extension of the layers of the stack the higherthe sensitivity/resolution of the sensing scheme is given that only asmall variation of the position of the magnet may cause an impact on themagnetization orientation of the ferromagnetic layers because such smallvariation in position still leads to a substantial change in magneticflux owed to the high gradient. In addition, it was observed that fortypical magnet geometries such as rectangular permanent magnets, anabsolute strength of the magnetic field at a given distance from themagnet increases with the gradient. Because there is an upper bound onthe strength of the magnetic field after which the magnetoresistiveelement saturates, the gradient of the magnetic field that caneffectively be used for sensing is limited.

According to an embodiment of the present invention, the dipole axis ofthe magnetic field source is aligned orthogonal to the plane defined bythe longitudinal axis and the transverse axis. Hence, the dipole axis isalso orthogonal to a sensing direction of the magnetoresistive elementwhich sensing direction is defined by the longitudinal extension of thelayers of the stack in direction of the longitudinal axis. Orthogonal inthis context shall include tolerances of +/−20° degrees, i.e. the dipoleaxis is supposed to be arranged with a range of 70° to 110° degrees withrespect to the plane defined by the longitudinal axis and the transverseaxis.

In one embodiment of the present invention, the magnetic field source isa permanent magnet of a size comparable to the size of the stack oflayers. This includes a width of the permanent magnet along thelongitudinal axis comparable to the longitudinal extension of the layersof the stack. In this context, comparability preferably includes a widthof the permanent magnet not more than ten times the longitudinalextension of the layers of the stack, and preferably not less than halfof the longitudinal extension of the layers of the stack. In a verypreferred embodiment, the magnet is of rectangular shape in a planedefined by the longitudinal axis and the vertical axis, and in anothervery preferred embodiment is of cuboid shape or rectangular prism shapecubic shape. According to another embodiment of the present invention,the magnetic field source is embodied as electromagnet.

The present idea is to place the magnetoresistive elements to both polesof the magnetic dipole. By doing so, completely new sensing regimes canbe achieved. In one embodiment, the sensors placed at the opposite polesof the magnetic field source may be used to suppress an inherentsensitivity of the magnetoresistive elements to motion in a verticaldirection. This can be a particularly powerful technique which is ofgreat importance in one-dimensional sensing applications. In anotherembodiment, the dual-pole sensing is used in a different read-outconfiguration to increase the sensitivity in the vertical axis,therefore enabling simultaneous sensing in two directions. Hence, theconcept of dual-pole sensing has many advantages.

In the figures, same or similar elements are denoted by the samereference signs.

FIG. 1 illustrates a schematic side cut of sensor arrangement accordingto an embodiment of the present invention comprising a firstmagnetoresistive element 1—in short first MR element 1, a secondmagnetoresistive element 2—in short second MR element 2, and a magneticfield source 3.

The first and second MR elements 1 and 2 are elements specificallyunderlying the giant magnetoresistivity phenomenon, wherein in thinmagnetic multilayers with one or more conductive layers in between spincoupling occurs. The first MR element 1 comprises a layer stack arrangedon a substrate 12 which layer stack includes at least a firstferromagnetic layer 111, a conductive and non-magnetic layer 112 and asecond ferromagnetic layer 113. Magnetic moments of the ferromagneticlayers 111 and 113 are naturally aligned antiparallel with respect toeach other when no external magnetic field is applied. In case anexternal magnetic field of sufficient strength is applied, magneticmoments become parallel in the ferromagnetic layers 111 and 113, i.e.the magnetization orientations in the ferromagnetic layers 111 and 113are aligned in parallel. An antiparallel magnetization orientation inthe ferromagnetic layers 111 and 113 result in a rather low mean freepath of electrons passing the layer stack leading to a rather highelectrical resistance in the layer stack. On the other hand, a parallelmagnetization orientation in the ferromagnetic layers 111 and 113 resultin a rather high mean free path of electrons passing the layer stackleading to a rather low electrical resistance in the layer stack. Thiseffect is based on the dependence of electron scattering on the spinorientation at the interfaces of the layers 111, 112 and 113. The sameholds for the second MR element 2 comprising a layer stack arranged on asubstrate 22 which layer stack includes at least a first ferromagneticlayer 211, a conductive and non-magnetic layer 212 and a secondferromagnetic layer 213.

The layers of each layer stack show a longitudinal extension L along thelongitudinal axis X. The layers also extend along the transverse axis Yinto the plane of projection. A current I may be applied to each layerstack during position sensing. The layers of the stacks are arrangedvertically, i.e. along vertical axis Z on top of each other.

The magnetic field source 3 may in the present embodiment be a permanentmagnet. Preferably, miniature ultra-thin magnetic dipoles may be usedfor enabling the stack of layers being exposed to magnetic fields with avery high gradient. A position sensing resolution of less than <200 pmover 100 kHz may be achieved. The magnetic field source 3 presently isof rectangular shape with a width W along the longitudinal axis X, adepth not visible along the transverse axis y, and a height H along thevertical axis Z. The width W of the magnet exceeds the longitudinalextension L of the layer stack.

In the present position, a dipole axis DA of the magnetic field source 3coincides with a sensor central axis SA of the MR elements 1 and 2 whichare preferably mechanically coupled and do not change position withrespect to each other. This means, the magnetic field source 3 iscentered above the MR elements 1 and 2. The magnetic field source 3provides a magnetic field illustrated in dashed lines which virtuallymay be separated into a first portion B1 and a second portion B2. As canbe derived from FIG. 1, magnetic field lines from both portions B1 andB2 may affect the layer stacks of the first and the second MR elements 1and 2 and as such impact the magnetization orientation of theferromagnetic layers 113 and/or 111, and 213 and/or 211. Both portionsB1 and B2 qualify by a high gradient when meeting the first MR element 1which is desired for achieving a high resolution because yet smallchanges in the position of the corresponding magnetic field source 3 maycause a realignment of the magnetic domain orientation in theferromagnetic layers 111, 113 which in turn may affect the conductivityof the layer stack. The same holds with respect to the second MR element2.

Hence, while in conventional position sensor arrangements the magneticfield source is aligned with its dipole axis DA in parallel to a sensingdirection X of the MR element 1 coinciding with the longitudinalextension of the layers, in the present embodiment the magnet fieldsource 3 is aligned with its dipole axis DA orthogonal to the sensingdirection X of the first and second magnetoresistive elements 1 and 2.For this reason, both a high gradient and a low strength of the magneticfield can be achieved at the same time. The low strength of the magneticfield is owed to the fact that the magnetic field lines go through zeromagnitude because the magnetic field in the subject portion whenprojected to the sensing direction changes direction.

FIG. 2 shows diagrams illustrating an impact of a magnetic field of amagnetic field source 3 on an MR element according to an embodiment ofthe present invention. In diagram 2 a) the magnetic field lines of amagnetic dipole comprising a first magnetic pole N and a second magneticpole S are shown wherein the effect is shown solely with respect to asingle MR element, a longitudinal extension of which is indicated byline B-B which MR element may be positioned at various distances D fromthe magnet as is indicated by the double arrow. The magnetic field linesare shown in a plane defined by the longitudinal axis X and the verticalaxis Z. In diagram 2 b), a corresponding flux density—also denoted asstrength of the magnetic field—is shown over the longitudinal axis X,and specifically is shown for different distances D between the magneticfield source 3 and the MR element. It can be derived from diagram 2 b)that the magnetic flux is zero at the location of the dipole axis X=XDwhile it is non-zero for X outside XD. In diagram 2 c), thecorresponding gradient of the magnetic field is shown over thelongitudinal axis X, and specifically is shown for different distances Dbetween the magnet and the magnetoresistive element with D1>D2. It canbe derived from diagram 2 c), that at the location of the dipole axisX=XD, the gradient has a maximum value while outside the dipole axisX=XD the gradient is lower in its absolute value. It further can bederived from diagram 2 b) that the bigger the distance D is the lowerthe magnetic flux density is while the closer the MR element is arrangedwith respect to the magnet the higher the magnetic flux density is. Onthe other hand, it can be derived from diagram 2 c) that the closer theMR element gets to the magnet, the higher the maximum gradient valuebecomes at X=XD.

In terms of resolution a high gradient and a low flux density is desiredat the same time. Diagram 2 c) in addition shows that a determination ofthe distance D may preferably also take into account the linearity ofthe gradient. It may be desired at the same time to provide a positionsensor sensing with a rather linear property over the sensing range.However, from diagram 2 c) it can be derived that the closer themagnetoresistive element is arranged with respect to the magnetic fieldsource 3, the higher the maximum gradient becomes, but after a point thegradient becomes less linear across the sensing range.

FIG. 3 depicts a diagram illustrating an impact of a magnetic field on amagnetoresistive element according to an embodiment of the presentinvention. It is assumed that in the x=0 longitudinal position themagnetic dipole is arranged centered on the magnetoresistive element 1such as shown in FIG. 1, i.e. the dipole axis DA coincides with thesensor axis SA. As can be derived from FIG. 3, in a region to the leftand right of x=0, there is a linear relation between the change inresistance and x. However, at some longitudinal position x magneticsaturation occurs such that the change in resistance is not indicativeof the longitudinal position x. However, it is only a rather shortsensing range in x, where linearity is given. Generally, the termsensing range is defined as the range in dimension X where no saturationoccurs.

On the other hand, the diagram in FIG. 3 shows the effect of varying thevertical distance between the magnetoresistive element and the magneticdipole: It can be derived that for short vertical distances a highsensitivity/slope can be achieved while for longer vertical distancesthe sensitivity drops. On the other hand, for longer vertical distances,the sensing range in x broadens, and saturation does not occur. Themagnetic dipole may be positioned relative to the magnetoresistiveelement at a vertical distance such that a large gradient of the appliedmagnetic field is achieved in the sensing range while at the same timegood linearity properties over the sensing range are provided. Sucharrangement may lead to a high bandwidth sensing but on the other handto a limited sensing range owed to the magnetic saturation.

With this insight and having returned to FIG. 1, it follows that in afirst embodiment in which the sensing direction is along thelongitudinal axis X and hence the position to determine is a position inX, variations of the position along the vertical axis Z may have heavyimpact on the measurement result. For example, the magnetic field source3 may be attached to an object while the first and the second MRelements 1 and 2 are stationary. The position of which object along thelongitudinal axis X is to be determined, however, the object may notalways take a fixed z-position but may suffer disturbances along thevertical axis Z. For this reason, it is suggested to provide the secondMR element 2 on the opposite end of the magnetic field source 3, i.e.facing the second magnetic pole S while the first MR element 1 faces thefirst magnetic pole N of the magnetic field source 3.

In the example of FIG. 1, it is assumed that a distance D1 between thefirst MR element 1 and the magnetic field source 3 is less than adistance D2 between the second MR element 2 and the magnetic fieldsource 3. However, a distance between the first and the second MRelement 1, 2 is fixed. By combining output signals of the first and thesecond MR element 1, 2, any variations in the vertical axis Z betweenthe magnetic field source 3 and the first and the second MR elements 1,2 can be levelled out.

This can be illustrated by the diagrams in FIG. 5. Diagram 5 a)illustrates an output signal R1 of the first MR element 1 of FIG. 1 forvarying distances D1 from the magnetic field source 3, wherein thedarker curves DC represent larger distances D1, e.g. the outmost darkcurve may represent a distance D1 of 400 μm, while the brighter curvesBC represent smaller distances D1, e.g. the innermost bright curve mayrepresent a distance D1 of 100 μm. The same is shown in diagram 5 b) forthe second MR element 2, wherein here the various curves are plotted forvarying distances D1, which on the other hand results in varyingdistances D2. The innermost dark curve DC represents a distance D1 of400 μm, i.e. a small distance D2, while the outmost bright curve BCrepresents a distance D1 of 100 μm which results in a larger distanceD2. Diagram 5 c) illustrates an addition of output signals R1+R2 forvarying distances D1, again under the assumption that the dark curve DCrepresent D1=400 μm, and the bright curve BC represents D1=100 μm.Hence, it can be derived from diagram 5 c) that in the present examplein a sensing range between 375 μm and 385 μm and 415 μm and 425 μm, theoutput signal R1+R2 is linear and independent from variations of themagnetic field source in z-direction.

A block diagram of this embodiment is shown in FIG. 4 comprising themagnetic field source 3 and a first and a second MR element 1, 2 facingthe magnetic poles N(orth) and S(outh), wherein the first output signalR1 of the first MR element 1 and the second output signal R2 of thesecond MR element 2 are added by a measurement unit 4, which in thisexample comprises a simple adder.

The diagram in FIG. 7 shows the curves for varying vertical positions ofthe magnetic field source 3, which is equivalent to the varying distanceD1 of FIG. 1 when subtracting the output signals R2 and R1 from eachother. In an x-range of 385 μm to 415 μm the sensor arrangement is inparticular sensitive to variations along the vertical axis Z. Hence, theposition to be sensed may also be a z-position instead of in x-position,or, in another embodiment, both x-position and z-position can be sensedsimultaneously.

A block diagram of a corresponding sensor arrangement is shown in FIG.6, which differs from the embodiment in FIG. 4 in that the measurementunit 4 contains a subtraction element for subtracting the second outputsignal R2 from the first output signal RE

In the schematic diagram of FIG. 8, only a lower portion of the sensorarrangement is shown comprising a magnetic field source 3. Instead of asingle first MR element 1, two first MR elements 11 and 12 are arrangedin a row along the longitudinal axis X, both MR elements 11 and 12facing the magnetic field source 3, and specifically its first magneticpole N. In this example, the dimension of the magnetic field source 3,which preferably is a permanent magnet, is such that the magnetic fieldnot only affects the first MR element 11, but also the other first MRelement 12 adjacent. For this purpose, it is preferred that the magneticfield source 3 has a width W along the longitudinal axis X exceeding thelongitudinal extension L of the first MR elements 11, 12.

Diagram 9 a) shows the two corresponding output signals R11 and R12 ofthe first MR elements 11, 12 as two impulses when that magnetic fieldsource 3 passes. When combining the output signals R11 and R12 bysubtraction, e.g. by subtracting R12 from R111 as is illustrated in FIG.8, the resulting measurement signal R11-R12 (“Sensor difference”) isdepicted as upper graph in diagram 9 a). It can be derived, that thelinear sensing range in x-direction is enhanced in comparison to using asingle MR element 11 only.

The curves in diagram 9 a) stem from an arrangement of the MR elements11 and 12 of FIG. 8 in x-direction that e.g. leaves a gap in between.Hence, the individual curves only show a small overlap which leads to anextension of the sensing range by a factor ˜2 compared to the sensingrange of a single MR element. The curves in diagram 9 b) instead stemsfrom a closer arrangement of the MR elements 11 and 12 in x-directionthan for diagram 9 a). Hence, the overlap of the individual curves islarger, which leads to a sensing range smaller than by factor ˜2compared to the sensing range of a single MR element. However, thesensitivity exceeds the one of diagram 9 a). Hence, it can be seen thatthe sensitivity and the sensing range can be tuned by how close the MRelements of a row are arranged with respect to each other.

Diagram 11 shows, how multiple MR elements—in the present examplefive—can be arranged in a row for enhancing the sensing range, andtherefore allowing position sensing in a wider sensing range x than withan individual MR element.

In the block diagram of FIG. 10, this sensing concept is shown for fourfirst MR elements 11, 12, 13 and 14, wherein the subtraction of theassociate output signals R12, R13 and R14 from output signalR11—including a scalar multiplication 41 of the output signals R13 andR14—leads to a measurement signal supporting an enhanced sensing range.

In FIG. 12, the sensing characteristic of an individual MR element isshown, on the one hand with unpinned magnetic layers as a straight line,and on the other hand with one pinned magnetic layer as a dashed line.From the characteristic of the MR element with the pinned magneticlayer, it can be derived that by adding the output signals of multiplefirst MR elements, in this example four, the linear sensing range can beenhanced. This is shown in FIG. 13.

FIG. 14 illustrates a lower portion of a sensor arrangement according toanother embodiment of the present invention. Here, a row of multiplefirst MR elements 11 to 1N is provided. However, the MR elements 11 to1N differ in their arrangement along the vertical axis Z. A middlemagnetoresistive element 1 m of the row is arranged at a closestvertical distance from the magnetic field source 3 amongst all the firstmagnetoresistive elements 11 to 1N. In contrast, the outmostmagnetoresistive first elements 11 and 1N of the row are arranged at afarthest vertical distance from the magnetic field source 3. Hence, thearrangement of the individual first MR elements 11 to 1N adjusts to theshape of the magnetic field especially if a center position of themagnetic field source 3 over the middle MR element 1 m as is shown inFIG. 14 is regarded as operating position. Hence, the MR elements 11 to1N follow a height profile in arrangement in vertical direction. FIG. 15illustrates a corresponding characteristic for a sensing arrangementwith a height profile.

The embodiments according from FIG. 8 to FIG. 13 are introduced forenhancing the sensing range and/or the sensitivity. The underlying ideais to use multiple MR elements positioned in a row in close proximity toone of the magnetic poles to increase the range and/or the resolution ofthe sensor arrangement. It is preferred, of course, that the arrangementof second MR elements opposite the second magnetic pole mirrors thearrangement of first MR elements.

However, the arrangement of multiple first MR elements and thecorresponding concepts of combining the respective output signals asintroduced in FIGS. 8 to 13 can also be applied independent from a oneor more second MR element 2, i.e. can be applied without one or moresecond MR elements 2 at the opposite magnetic pole. Hence, in oneembodiment, a configuration of two or more sensors with a differentialread-out is proposed which increases the sensing range and/or theresolution by exploiting the characteristics of unpinned GMR valves.Further, a concept of height-profiled sensors and sensing elements isintroduced which enables shaping of the sensor in the vertical directionaccording to the magnetic field and avoids the saturation of the sensingelements. By doing so, the range of the sensor can be significantlyincreased without losing the sensitivity and resolution. Furthermore, aconcept for large-range sensing with pinned GMR valves is presented.Here, the particular sensor characteristics of pinned GMR valves areused to significantly extend the sensing range in an additive read-outscheme.

FIG. 16 illustrates another embodiment of a sensor arrangement accordingto the present invention. Presently, the sensor arrangement comprisesfour first MR elements 11 to 14 and four second MR elements 21 to 24.However, the number can easily be extended. Again, the magnetic fieldsource 3 in form of a permanent magnet is arranged between the first andsecond MR elements 1 m and 2 n, and is movable in x-direction. In thisembodiment, the magnetic field source 3 is dimensioned relative to themagnetoresistive elements 1 m, 2 n such that the magnetic field onlyaffects a single one of the first and a single one of the second MRelements, i.e. exactly these first and second MR elements 1 m and 1 nthe magnetic field source 3 is located in between during the passage inx-direction which are MR elements 13 and 23 in FIG. 16. This is achievedby dimensioning a width W of the magnetic field source less than alength L of any one of the MR elements 1 m, 2 n. In such arrangement, MRelements 12, 14 and 22, 24 adjacent to the first and second MR elements13 and 23 that presently monitor a change in resistance in form of apulse when the magnetic field source 3 passes do not provide suchsignificant change in their output signals. Therefore, the outputsignals of the various MR elements of one row are not mixed with one andanother but each one is individually evaluated as to the appearance of apulse indicating a passing of the magnetic field source 3. With theknowledge of the positions of the individual MR elements in thesequential arrangement of the first or the second MR elements 1 m, 2 n aposition of the magnetic field source 3 along the longitudinal axis Xcan be derived.

FIG. 17 illustrates a block diagram of a sensor arrangement according toanother embodiment of the present invention. Here, the concepts of theembodiments of FIGS. 4 and 8 are merged. Accordingly, two first MRelements 11 and 12 are arranged in a row facing the first magnetic poleN, while two second MR elements 21 and 22 are arranged in a row facingthe second magnetic pole S. The output signals from the MR elements of acommon row are subtracted from each other, while the results of thesesubtractions are added. Hence, the overall measurement signal representsa position signal in X that is compensated for variations/disturbancesin Z, while at the same time a sensing range in X is increased byproviding two first and two second MR elements 11, 12 and 21, 22 next toeach other.

Embodiments of the present invention may be applicable to positionsensing in industry, to lithography, and specifically in connection withsemiconductors such as the manufacturing, EDA and testing ofsemiconducting devices, and specifically of micro- and/ornano-electromechanical devices. Any such position sensor may transmitits result wire bound or wireless to an evaluation unit.

1. A sensor arrangement for position sensing, comprising a magneticfield source providing a magnetic field with a first magnetic pole (N)and a second magnetic pole (S), and two or more magnetoresistiveelements arranged in the magnetic field in a row along a longitudinalaxis (X) and having a gap between each magnetoresistive element in therow, said row of two or more magnetoresistive elements facing the firstmagnetic pole (N); a measurement unit, wherein the row of two or moremagnetoresistive elements is arranged in the magnetic field and eachproviding an output signal dependent on a position of themagnetoresistive elements relative to the magnetic field source, whereinthe measurement unit is configured to determine a position of themagnetic field source (3) relative to the row of two or moremagnetoresistive elements dependent on the output signals.
 2. The sensorarrangement of claim 1, wherein each of the two or more magnetoresistiveelements of the row comprises a stack of layers including at least aconductive layer in between two magnetic layers which layers have alongitudinal extension (L) along a longitudinal axis (X) and a lateralextension along a transverse axis (Y), wherein the magnetic field sourcehas a dipole axis (DA) defined by the first and the second magnetic pole(N, S) extending along a vertical axis (Z) orthogonal to a plane definedby the longitudinal axis (X) and the transverse axis (Y).
 3. The sensorarrangement of claim 2, wherein the magnetic field source is movablerelative to the row of two or more magnetoresistive elements along thelongitudinal axis (X), a position (x) thereof along the longitudinalaxis (X) is to be sensed by the sensor arrangement, and wherein themeasurement unit is configured to determine the position (x) along thelongitudinal axis (X) by computing a difference between each saidprovided output signal.
 4. The sensor arrangement of claim 1, comprisingadditional two or more magnetoresistive elements arranged in themagnetic field in an additional row along the longitudinal axis andhaving a gap between each magnetoresistive element in the additionalrow, said additional row of additional two or more magnetoresistiveelements facing the second magnetic pole (S).
 5. The sensor arrangementof claim 1, wherein the magnetic field source is dimensioned relative tothe row of two or more magnetoresistive elements such that the magneticaffects a single magnetoresistive element of the two or moremagnetoresistive elements at a time but not adjacent firstmagnetoresistive elements of the row, and wherein the magnetic fieldsource is a permanent magnet which has a width (W) less than thelongitudinal extension (L) of a magnetoresistive element in the row. 6.The sensor arrangement of claim 1, wherein the measurement unit isconfigured to identify the single first magnetoresistive element out ofthe two or more magnetoresistive elements that shows a change in itsfirst output signal which change results from the magnetic field sourcepassing by the single first magnetoresistive element, and wherein themeasurement unit is configured to derive the position (x) along thelongitudinal axis (X) from a known position of the single firstmagnetoresistive element within the row of the two or more firstmagnetoresistive elements.
 7. The sensor arrangement of claim 1, whereinthe magnetic field source is dimensioned relative to the two or moremagnetoresistive elements such that the magnetic field not only affectsa single of the two or more first magnetoresistive elements but alsoadjacent first magnetoresistive elements, and wherein the magnetic fieldsource is a permanent magnet which has a width (W) along thelongitudinal axis (X) exceeding the longitudinal extension (L) of amagnetoresistive element in the row.
 8. The sensor arrangement of claim3, wherein a magnetization orientation of both of the magnetic layers ofeach the two or more magnetoresistive elements of the row is unpinned,wherein the measurement unit is configured to subtract first outputsignals (R1) of adjacent first magnetoresistive elements (1) from eachother, and wherein the measurement unit is configured to determine theposition (x) along the longitudinal axis (X) dependent on a resultingdifference signal.
 9. The sensor arrangement of claim 1, comprisingmultiple magnetoresistive elements arranged in the row, said multiplemagnetoresistive elements being offset from each other along thevertical axis (Z).
 10. The sensor arrangement of claim 9, wherein amiddle first magnetoresistive element (1 m) is arranged at a closestvertical distance from the magnetic field source (3) amongst themultiple magnetoresistive elements of the row, and wherein outmost firstmagnetoresistive elements (1) are arranged at a farthest verticaldistance from the magnetic field source (3) amongst the multiple firstmagnetoresistive elements of the row.
 11. The sensor arrangement ofclaim 1, wherein one of the magnetoresistive elements of the row and themagnetic field source (3) is coupled to an object (5), the position ofwhich object (5) is to be sensed by the sensor arrangement.
 12. A methodfor determining the position of an object, comprising: coupling one of amagnetic field source (3) providing a magnetic field with a firstmagnetic pole (N) and a second magnetic pole (S) and two or moremagnetoresistive elements with the object, said two or moremagnetoresistive elements arranged in the magnetic field in a row alonga longitudinal axis (X) and having a gap between each magnetoresistiveelement in the row, said row of two or more magnetoresistive elementsfacing the first magnetic pole (N); arranging the magnetic field source(3) such that the first magnetic pole (N) faces the two or moremagnetoresistive elements of the row to form a sensor arrangement,receiving, at a measurement unit, an output signal from each of the twoor more magnetoresistive elements dependent on their position (x)relative to the magnetic field source (3), and determining, by themeasurement unit, a position of the object (5) dependent on the receivedoutput signals.
 13. The method as claimed in claim 12, wherein each ofthe magnetoresistive elements of the row comprises a stack of layersincluding at least a conductive layer in between two magnetic layerswhich layers have a longitudinal extension (L) along a longitudinal axis(X) and a lateral extension along a transverse axis (Y), said methodcomprising: defining a dipole axis (DA) of the magnetic field source bythe first and the second magnetic pole (N, S) extending along a verticalaxis (Z) orthogonal to a plane defined by the longitudinal axis (X) andthe transverse axis (Y).
 14. The method as claimed in claim 13, furthercomprising: moving the magnetic field source (3) relative to the firstrow of two or more magnetoresistive elements along the longitudinal axis(X), a position (x) thereof along the longitudinal axis (X) is to besensed by the sensor arrangement, and determining, by the measurementunit, the position (x) along the longitudinal axis (X) by computing adifference between each said provided output signal.
 15. The method asclaimed in claim 13, further comprising: arranging additional two ormore magnetoresistive elements in the magnetic field in an additionalrow along the longitudinal axis and having a gap between eachmagnetoresistive element in the additional row, said additional row ofadditional two or more magnetoresistive elements facing the secondmagnetic pole (S).
 16. The method as claimed in claim 15, furthercomprising: moving the magnetic field source (3) relative to the firstrow of two or more magnetoresistive elements along the longitudinal axis(X), a position (x) thereof along the longitudinal axis (X) is to besensed by the sensor arrangement, and determining, by the measurementunit, the position (x) along the longitudinal axis (X) by computing asubtraction of each said provided output signal of a magnetoresistiveelement in a common row and adding the results of the subtractions. 17.The method as claimed in claim 1, wherein the magnetic field source (3)is dimensioned relative to the two or more magnetoresistive elements ofthe row such that the magnetic field only affects a single (1 a) of themultiple first magnetoresistive elements (1) at a time but not adjacentfirst magnetoresistive elements (1 b, 1 c), the magnetic field source(3) being a permanent magnet which has a width (W) less than thelongitudinal extension (L) of a magnetoresistive element, said methodfurther comprising: identifying, by the measurement unit, the singlemagnetoresistive element out of the two or more magnetoresistiveelements of the row that shows a change in its first output signal (R1)which change results from the magnetic field source (3) passing by thesingle first magnetoresistive element (1 a), and deriving, by themeasurement unit, the position (x) along the longitudinal axis (X) froma known position of the first magnetoresistive element within the row ofmagnetoresistive elements.
 18. The method as claimed in claim 13,wherein the magnetic field source (3) is dimensioned relative to themultiple first magnetoresistive elements (1) such that the magneticfield not only affects a single (1 a) of the multiple firstmagnetoresistive elements (1) but also adjacent first magnetoresistiveelements (1 b, 1 c), the magnetic field source (3) being a permanentmagnet which has a width (W) along the longitudinal axis (X) exceedingthe longitudinal extension (L) of the first magnetoresistive element(1), and a magnetization orientation of both of the magnetic layers ofthe two or more magnetoresistive elements of a row is unpinned, saidmethod further comprising: subtracting, by the measurement unit, firstoutput signals (R1) of adjacent first magnetoresistive elements (1) fromeach other, and determining, by the measurement unit, the position (x)along the longitudinal axis (X) dependent on a resulting differencesignal.
 19. The method as claimed in claim 13, wherein a magnetizationorientation of one of the magnetic layers of the two or moremagnetoresistive elements (1) is pinned, said method further comprising:adding, by the measurement unit, the first output signals (R1) ofadjacent first magnetoresistive elements (1), and determining, by themeasurement unit, the position (x) along the longitudinal axis (X)dependent on a resulting sum signal.
 20. The method as claimed in claim13, further comprising: arranging multiple first magnetoresistiveelements (1) in the row offset from each other along the vertical axis(Z), wherein a middle magnetoresistive element is situated at a closestvertical distance from the magnetic field source amongst the multiplefirst magnetoresistive elements of the row, and outmost magnetoresistiveelements of the row are arranged at a farthest vertical distance fromthe magnetic field source amongst the multiple magnetoresistive elementsof the row.